Recreational vehicles, buses, boats and other vehicles with portable living accommodations are commonly equipped with holding tanks for both gray water and sewage. Periodically these tanks must be drained into a sanitary sewage system. The holding tanks are typically discharged into the sewer through a compressible or collapsible hose which can be expanded and fitted both to the holding tank outlet and to an inlet for the sewer. Gravity then induces flow between the holding tank and the sanitary sewage system. In addition to serving in this capacity when the holding tank is to be drained, there are some recreational vehicle facilities with sewer inlets at individual parking locations or campsites so that the sewer hose can connect the recreational vehicle to the sewer for an extended duration. In this arrangement, the waste matter need not be held in the sewage holding tank, but may pass directly to the hose and into the sewer system. The manual connection and disconnection of the sewer hose between vehicle holding tank and sewer inlet can be unsanitary and unpleasant, particularly when there are difficulties with adapters or fittings connecting the sewer hose to inlets and outlets or attendant to cleaning and storage of the sewer hose upon disconnection, as when leaving a campsite.
In order to serve its purpose, a sewer hose of this type should satisfy a number of criteria. These criteria include accommodating useful fittings at each end of the hose for fastening to the holding tank outlet, to the sewer inlet, or to another hose when it is necessary to join two sewer hoses for extended length. In addition, the sewer hose should be made of durable material that is chemically resistant so that it will not be damaged by exposure to sewage, and gray water, and sanitizing agents and should be easily cleaned. The sewer hose should also generally be expandable to a significant length when in use yet be collapsible for storage in a relatively compact form as most sewer hoses are stored in either an external cavity on the recreational vehicle or within a sealable plastic container. The sewer hose should be flexible enough to be easily positioned yet sufficiently rigid to maintain the consistent downward pitch from vehicle holding tank to sewer inlet needed for gravity flow. The sewer hose should be resistant to collapse and should resist abrasion and puncture and remain leak free through many cycles of use.
Hoses for this purpose have been in use for many years and have almost been uniformly made of strips of flexible vinyl film which are continuously extruded or wound in a helical pattern over a helical steel coil and glued or heat sealed to form a helically corrugated tube. A manufacturing process for hose tubing of this type is described in U.S. Pat. No. 6,024,134 to Akedo, et al. Higher quality sewer hose may utilize polyolefin or polypropylene film.
After manufacture of the hose, rigid couplings are threaded into the ends of the hose to facilitate connections to holding tanks and sewers. In some instances the couplings are permanently glued to the ends of the sewer hose, thereby necessitating disposal when the sewer hose is damaged or worn. Other couplings are removable. Since current sewer hoses have either left hand or right hand helixes, the removable couplings are made with corresponding left hand or right hand fittings and the two types are not entirely interchangeable. The structure of these hoses is similar to a plastic or vinyl covered light weight spring, such as the metal spring forming a traditional SLINKY spring toy. When left free, the hose tends to contract and the hose will not generally reach its nominal length unless under tension. The hoses are supple and do not support their own weight or hold a shape or position. Therefore, in order to maintain gravity flow, rigid supports may need to be placed under the hoses.
More recently, higher quality sewer hoses have been manufactured where the steel coils are coated with a first color of PVC prior to being wound with polyolefin or polypropylene tape of a second color. In this fashion, should the hose become abraded, as by dragging along the ground, damage penetrating the outer tape layer can be observed by contrast in color. In addition, the steel coil is not immediately exposed to moisture when the outer tape is abraded so that rust does not immediately ensue. This allows the sewer hose to be repaired or replaced in a timely fashion.
Furthermore, some of these polyolefin or polypropylene hoses have been made so that the helical corrugations can be expanded and remain open and provide the hose with sufficient rigidity not to require external support. However, these improved hoses are relatively expensive, typically costing between about 2-5 times the price of the ordinary vinyl tape hose. The tapes of all of these hoses are applied in several layers in order to achieve a total wall thickness of between about 15-25 mils. In some instances, the outer layer of tape has been formulated for UV resistance.